A 2016 study by M. Benjamin Nelson, et al, explored the accuracy of a number of consumer-grade step/activity monitors by having 30 research subjects do various activities while wearing various activity monitors as well as the Omron HJ-720IT, which the researchers considered to have “been shown to be a valid step counter at variable walking speeds in structured settings.”
Frankly, that’s a bit odd because I would view the Omron HJ-720IT as a consumer grade step counter as well. You can buy them on Amazon and I’ve owned about half a dozen of them over the years.
So the researchers had the subjects where the Fibit One, Fitbit Zip, Fitbit Flex, Jawbone UP24 and the Omron device as well as a portable metabolic analyzer.
The study found that the “consumer grade” devices performed as well as the Omron as far as step counting, but that they were all relatively unreliable for measuring energy expenditure (the ridiculous “calorie counting” measure that many of these devices give the user).
They also found that all of the counters, including the Omron, had significant error rates in measuring steps from “household activities” (which they tended to undercount), but did fairly well at measuring steps from actual walking and jogging.
All PA monitors predicted EE within 8% of COSMED [indirect calorimetry] for sedentary activity but overestimated EE by 16%-40% during ambulatory activity. All monitors except the Fitbit Flex (within 8% of criterion) underestimated EE by 27%-34% during household activity. EE predictions were accompanied with MAPE >10%. For household activity, the Fitbit Flex estimated steps within 10% of researcher-counted steps; all other monitors underestimated steps by 35%-64%. All monitors estimated steps within 4% of researcher-counted steps and displayed MAPE <10% during ambulatory activity. The Omron underestimated household steps by 74% but was within 1% for ambulatory steps. All monitors severely underestimated EE and steps during cycling.
CONCLUSION: Consumer-based PA monitors should be used cautiously for estimating EE, although they provide accurate measures of steps for structured ambulatory activity, similar to validated pedometers.
